1. Field of the Invention
The present invention generally relates to a semiconductor-manufacturing method, particularly to a method of parallel shift operation of multiple reactors wherein gases are continuously supplied to the reactors.
2. Description of the Related Art
A plasma-enhanced atomic layer deposition (PEALD) process typically repeats the following four steps as illustrated in FIG. 1:
In step 1 (Precursor feeding), a precursor gas is supplied into a reactor chamber (RC) and the precursor is adsorbed onto a wafer surface. In step 2 (Purge), non-adsorbed precursor is removed from the reactor chamber. In step 3 (Plasma treatment), the adsorbed surface is activated by RF plasma for reaction of the precursor with a reactant gas. In step 4 (Purge), non-reacted precursor and by-products are removed from the surface. In the above, during the steps, the reactant gas continuously flows. Equipment for the PEALD process requires the following components as illustrated in FIG. 3:
An RF generator (single or dual frequency): 1 device (4)/1 RC;
A precursor gas line: 1 line (1)/1 RC (if the process requires switching and flowing different precursors, a different line (2) is required for each precursor);
A reactant gas line: 1 line (3)/1 RC; and
An RC pressure control valve and exhaust line: 1 set (6, 7)/1 RC.
The required components must be changed when expanding the system from one RC to multiple RCs. By simple expansion, a two-RC system requires the following components as illustrated in FIG. 4:
An RF generator (single or dual frequency): 2 devices (4, 4′)/2 RCs;
A precursor gas line: 2 lines (1, 1′)/2 RCs (if the process requires switching and flowing different precursors, a different line is required for each precursor per RC);
A reactant gas line: 2 lines (3, 3′)/2 RCs; and
An RC pressure control valve and exhaust line: 2 sets (6, 7, 6′,7′)/2 RCs.
Considering the above component redundancy, the system requirements can be modified, depending on the precursor supply system, the architecture of process sequence, and the process controllability between two RCs.
The precursor supply system is classified into the following two types:
(I) By on/off control of a precursor flow, precursor supply is controlled as illustrated in (I) in FIG. 5.
(II) By switching a precursor flow and an inactive gas flow while maintaining the same flow rate, precursor supply is controlled as illustrated in (II) in FIG. 5.
In the on-off flow control system, a liquid precursor is vaporized in a tank 41, a carrier gas is introduced into the tank 41 through a line 43, and when a valve 42 is closed, no flow goes out from the tank 41 through a line 44 as illustrated in (a) in FIG. 5. When the valve 42 is open, the carrier gas carries the vaporized precursor and flows out together from the tank 41 through the line 44 as illustrated in (b) in FIG. 5. By the on/off control of precursor flow, a total gas flow rate and an RC pressure become altered. Therefore, this flow control system is not adopted in the case where the RC pressure difference between RCs could cause a problem (e.g. improper precursor gas inflow goes to a wrong RC via a shared exhaust line due to the pressure difference between the RCs). In the switching flow control system, a liquid precursor is vaporized in a tank 51, a carrier gas is introduced into the tank 51 through a line 53 via a valve 56 since a valve 55 is closed. The carrier gas carries the vaporized precursor and flows out together from the tank 51 through a line 54 via a valve 57 as illustrated in (d) in FIG. 5. However, when the valve 55 is open, and the valves 56, 57 are closed, only the carrier gas flows through the lines 53, 54 as illustrated in (c) in FIG. 5. By switching a precursor and an inactive gas flow, a total flow rate and an RC pressure can substantially be fixed and an RC pressure is easily controlled by an automatic pressure controller (not shown). In this flow control system, since there is no substantial pressure difference between the RCs, although the RCs share an exhaust line, there is substantially no interplay between the RCs. A typical process sequence using the switching flow control system is illustrated in FIG. 2. The difference from the process sequence shown in FIG. 1 is that in steps 2, 3, and 4, upon switching from the precursor to the inactive gas, the inactive gas flows continuously from step 1 at the same flow rate as that of the precursor in step 1.
The architecture of process sequence is classified into the following two types.
(1) Concurrent processing between RC1 and RC2 as illustrated in (1) in FIG. 6;
(2) Alternate processing between RC1 and RC2 as illustrated in (2) in FIG. 6.
Concurrent processing is simple. In a PEALD process, the alternate processing can be selected to reduce system components by eliminating duplicate (simultaneous timing) operation of a single resource used only in a specific step. For example, by eliminating overlapping plasma treatment between two RCs, a single RF generator can be shared between the two RCs. In alternate processing, the same operation is conducted in two RCs alternately, wherein independent process step control is required for each of the RCs.
The process controllability between two RCs is classified into the following two types according to whether different processing cycles between two RCs can or cannot be set.
(A) Different processing cycles between two RCs can be set;
(B) Different processing cycles between two RCs cannot be set (only the same processing cycles can be set).
There are some advantages of setting the different processing cycles between two RCs. First, processes under different conditions (e.g., film thickness) of deposition can be performed simultaneously at the respective RCs. Second, an RC-to-RC mismatch can be adjusted by setting different processing cycles between the RCs. It should be noted that the system capable of alternate processing is naturally able to process different cycles between two RCs since independent process step control is required for each of the RCs capable of alternate processing.
The precursor supply system ((I): on-off flow control system; (II): switching flow control system), the architecture of process sequence ((1): concurrent processing; (2): alternate processing), and the process controllability between two RCs ((A): different cycles; (B): identical cycles) can be combined in multiple ways.
FIG. 7 illustrates a two-reactor system with an on-off flow control system (I), concurrent processing (1), and the capability of different cycles (A), wherein a precursor line 1, a precursor line 2, and a reactant gas line 3 are shared by a reaction chamber 4 and a reaction chamber 4′. However, in order to have the capability of different cycles between the reaction chambers 4, 4′, different RF generators 5, 5′, different pressure control valves 6, 6′, and different exhaust lines 7, 7′ are provided to the reaction chambers 4, 4′, respectively.
FIG. 8 illustrates a two-reactor (two-RC) system with an on-off flow control system (I), concurrent processing (1), and incapability of different cycles (B), wherein a precursor line 1, a precursor line 2, a reactant gas line 3, a pressure control valve 6, and an exhaust line 7 are shared by a reaction chamber 4 and a reaction chamber 4′. Although an RF generator can be shared by the reaction chambers 4, 4′, different RF generators 5, 5′ are used to ensure the same effective power between RCs. Since the process is concurrent without the capability of different cycles, all of the components (except for the RF generators) can be shared by the two reaction chambers.
FIG. 9 illustrates a two-reactor (two-RC) system with the on-off flow control system (1) and alternate processing (2), wherein a precursor line 1, a precursor line 2, and a reactant gas line 3 are shared by a reaction chamber 4 and a reaction chamber 4′. In order to perform alternate processing, the flows of gases are controlled by on-off valves 8, different pressure control valves 6, 6′, and different exhaust lines 7, 7′ are provided to the reaction chambers 4, 4′, respectively. Although different RF generators can be used in the reaction chambers 4, 4′, an RF generator 5 provided with a switch for switching the reaction chambers 4, 4′ is shared by the reaction chambers 4, 4′.
FIG. 10 illustrates a two-reactor (two-RC) system with a switching flow control system (II), concurrent processing (1), and capability of different cycles (A), wherein a reactant gas line 3 is shared by a reaction chamber 4 and a reaction chamber 4′. In order to perform different cycles between the reaction chambers 4, 4′, different precursor/inactive gas lines 11, 11′ (with a fixed flow rate), different precursor/inactive gas lines 12, 12′ (with a fixed flow rate), and different RF generators 5, 5′ are provided to the reaction chambers 4, 4′, respectively. Regardless of whether the cycles are different between the reaction chambers 4, 4′, the total flows of gases of the reaction chambers 4, 4′ are the same because of the switching flow control system (i.e., the flow rate is fixed), and thus, a pressure control valve 6 and a exhaust line 7 are shared by the reaction chambers 4, 4′.
FIG. 11 illustrates a two-reactor (two-RC) system with a switching flow control system (II), concurrent processing (1), and incapability of different cycles (B), wherein a precursor/inactive gas line 11 (with a fixed flow rate), a precursor/inactive gas line 12 (with a fixed flow rate), a reactant gas line 3, a pressure control valve 6, and a exhaust line 7 are shared by a reaction chamber 4 and a reaction chamber 4′. Although an RF generator can be shared by the reaction chambers 4, 4′, different RF generators 5, 5′ are used to ensure the same effective power between RCs. Since the process is concurrent without the capability of different cycles, all of the components (except for the RF generators) can be shared by the two reaction chambers.
FIG. 12 illustrates a two-reactor (two-RC) system with a switching flow control system (II) and alternate processing (2), wherein a reactant gas line 3 is shared by a reaction chamber 4 and a reaction chamber 4′. In order to perform alternate processing in the reaction chambers 4, 4′, different precursor/inactive gas lines 11, 11′ (with a fixed flow rate), and different precursor/inactive gas lines 12, 12′ (with a fixed flow rate) are provided to the reaction chambers 4, 4′, respectively. Regardless of whether the processing is performed in the reaction chambers 4, 4′ alternately, the total flows of gases of the reaction chambers 4, 4′ are the same because of the switching flow control system (i.e., the flow rate is fixed), and thus, a pressure control valve 6 and an exhaust line 7 are shared by the reaction chambers 4, 4′. Although different RF generators can be used in the reaction chambers 4, 4′, an RF generator 5 provided with a switch for switching the reaction chambers 4, 4′ is shared by the reaction chambers 4, 4′.
Table 1 below summarizes the above combinations and the required minimum components.
TABLE 1RC pressurePrecursor lineReactant gascontrol valveCombinationFIG.RF generatorper precursorlineand exhaust line(I)-(1)-(A)72 sets/2 RCs1 sets/2 RCs1 sets/2 RCs2 sets/2 RCs(I)-(1)-(B)82 sets/2 RCs1 sets/2 RCs1 sets/2 RCs1 sets/2 RCs(I)-(2)91 sets/2 RCs1 sets/2 RCs1 sets/2 RCs2 sets/2 RCs(II)-(1)-(A)102 sets/2 RCs2 sets/2 RCs1 sets/2 RCs1 sets/2 RCs(II)-(1)-(B)112 sets/2 RCs1 sets/2 RCs1 sets/2 RCs1 sets/2 RCs(II)-(2)121 sets/2 RCs2 sets/2 RCs1 sets/2 RCs1 sets/2 RCs
As shown in Table 1, in order to be capable of alternate processing (2) or different cycles (A), the system requires two sets of at least one of precursor lines or RC pressure control valves and exhaust lines.
The above examples are based on PEALD. However, any cyclic deposition (e.g., cyclic CVD, thermal ALD, radical-enhanced ALD, etc.) using multiple reaction chambers has similar problems in increasing the number of system components.
Further, in any cyclic deposition, film deposition processes based on chemical reaction typically use separate supply of reactant gas(es) during film deposition, because unwanted chemical reaction should be avoided between precursor and reactant gas(es), or because reactant gases need to be supplied separately for specific chemical reactions. For separate reactant gas supply, removing the reactant gas remaining in the reaction chamber before introducing another reactant gas is required. It requires additional transition time (e.g., >1 sec) at each and every reactant supply in order to remove the remaining reactant gas by purging the reaction chamber or pumping out the reaction chamber. Typically, the transition time includes stopping reactant gas supply, removing the remaining reactant gas by purging or pumping out the reaction chamber, and supplying and stabilizing a different reactant gas. Thus, changing gases increases process cycle time, lowering productivity. Further, since inactive gas is used for changing reactant gases and purging, the reactant gas is diluted by the inactive gas, and the partial pressure of the reactant gas is lowered, lowering chemical reaction speed.
FIG. 17 illustrates a conventional process sequence used for cyclic deposition using two reaction chambers based on concurrent processing, wherein the steps of supplying reactant gas A to each of reaction chambers 1 and 2, purging the reaction chambers 1 and 2, supplying reactant gas B to each of the reaction chambers 1 and 2, and then purging the reaction chambers 1 and 2, are repeated. FIG. 17 is overly simplified, and each supply pulse of reactant gas does not start and end as sharply as indicated in FIG. 17. The transition time and the dilution of reactant gas are unavoidable in conventional cyclic deposition. In this disclosure, the “reactant gas” refers to any gas participating in a chemical reaction of deposition or formation of a film, including a precursor in the broad sense. In the narrow sense, the “reactant gas” refers to any gas reacting with a precursor for deposition or formation of a film.
Any discussion of problems and solutions involved in the related art has been included in this disclosure solely for the purposes of providing a context for the present invention, and should not be taken as an admission that any or all of the discussion were known at the time the invention was made.